Nourishing Shoal
Instant — Arcane
You may exile a green card with mana value X from your hand rather than pay this spell's mana cost.
You gain X life.
Greg Staples
Ultimate Masters (UMA)
• #175Rulings
If a card in a player's hand has {X} in its mana cost, X is considered to be 0.
(wotc • 2018-12-07)
If a spell has {X} in its mana cost, include the value chosen for that X when determining the mana value of that spell, even if it was cast for an alternative cost and no mana was spent on X.
(wotc • 2018-12-07)
Rulings
If a card in a player's hand has {X} in its mana cost, X is considered to be 0.
(wotc • 2018-12-07)
If a spell has {X} in its mana cost, include the value chosen for that X when determining the mana value of that spell, even if it was cast for an alternative cost and no mana was spent on X.
(wotc • 2018-12-07)